Usually surface treatment is applied to the surface of cold-rolled steel plates, etc. for anticorrosion and preservation of fine appearance.
That is, because a considerable time passes before such various types of steel plates and so on are processed and used, they are coated with an antirust oil or chemically treated or are packed in vaporable antirust paper or are otherwise treated to prevent rust. Any of these prior art methods for anticorrosion, however, has the following drawbacks.
The application of antirust oil will incur, not to mention stickness of oil, the necessity for a degreasing step when the steel plates are in use, followed by the treatment of the exhausted degreasing solution, which is troublesome.
In addition, welding or like processing of materials with antirust oil applied thereto presents problems in that the electrodes become dirty, fuming becomes significant and the preservation of a good working circumstances is adversely affected.
Already publicly known water soluble antirust agents, for example, sodium nitrite, sodium borate, aromatic carboxylic acids, imidazoles, amines and surfactants are used alone or in combination. However, their antirust effect is useful mainly in water or in the air, and is rather poor when the steel plates contact one another in a wet atmosphere or under conditions where water is attached to them or when they are stacked at high temperature and high humidity, namely, in a wet box as specified by JIS Z-0228. Further, there are antirust agents with higher aliphatic amines or higher fatty acids incorporated therein. However, they also have drawbacks that their drying characteristics are bad and that a removal step is required as in the case of the use of antirust oil.
The inventors of the present invention have already discovered that 1-hydroxybenzotriazole has an excellent antirust effect for steel stocks as is described in Japanese patent publication No. 27694/78. However, it has been found that there is in this case a weakness that the discoloration or staining is produced in some cases if water is dropped on a treated steel plate, and another treated one is stacked thereon and allowed to stand at high temperature and high humidity atmosphere, although their antirust properties are very excellent after they are subjected to hot-air drying.
The present invention has overcome these drawbacks of the prior art methods and has further made it possible to exert an extremely good antirust effect without necessity for any further treatment in the subsequent steps.